How to troubleshoot a battery draining issue in an Audi A4?

My Audi A4's battery keeps draining even when the car is not in use. What could be the possible causes for this issue and how can I troubleshoot it?

First, make sure all the lights and electronic systems in your car are turned off when the car is not in use.

Check the battery connections and terminals for any corrosion or looseness. Clean and tighten them if necessary.

You may also want to check for any faulty electrical components or wiring that may be draining the battery.